Researchers affiliated with the Assignee Senomyx as well as a research group at the University of California have previously reported the identification and functionalization of a family of G-protein coupled receptors involved in mammalian taste referred to as the T1R family. This family of taste receptors consists of 3 members, T1R1, T1R2 and T1R3. These receptors are expressed in different tissues including the tongue, organs in the digestive system as well as in other types of tissues and modulate sweet and umami taste.
In particular, these entities have demonstrated using mammalian cells that express the T1R1 and T1R3 as well as a suitable G protein, e.g., a promiscuous G protein or a chimeric G protein, that the T1R1 and T1R3 receptors dimerize to form a heteromeric taste receptor comprising T1R1 and T1R3 polypeptides that responds to umami (savory) taste compounds. These same entities have similarly demonstrated that when the T1R2 and T1R3 polypeptides are expressed in a cell that comprises a suitable G protein, e.g., a promiscuous G protein or a chimeric G protein, that the T1R2 and T1R3 polypeptides dimerize to form a heteromeric taste receptor comprising the T1R2 and T1R3 polypeptides that responds to sweet taste compounds. This research is reported in various scientific articles including Li et al., Proc. Natl. Acad. Sci, USA 2002, April 12 99(7)4692-4696; Xu et al., Proc. Natl. Acad. Sci, USA 2004, Sep. 28, 101(36)14652863; as well as numerous patents assigned to Senomyx and the University of California.
Also, these entities and others have disclosed the use of recombinant and endogenous cells which co-express either T1R2 and T1R3 polypeptides or T1R1 and T1R3 polypeptides to respectively identify compounds that modulate sweet or umami taste. Also, T1R polypeptides have been suggested to be involved in glucose transport, food sensing and motility, and insulin responses.
Assays using T1R2/T1R3 and T1R1/T1R3 heteromers have resulted in the identification of numerous compounds that modulate sweet or umami taste some of which have been approved for use in foods for human consumption. While these assays are predictive as to the potential effect of the identified compounds on a particular taste modality associated with T1R-associated taste, i.e., sweet or umami taste, one recurring problem which has been observed is that the “hits”, i.e., the group of identified T1R2/T1R3 or T1R1/T1R3 modulatory compounds often contain “false positives”. That is to say, while the compounds demonstrably modulate the activity of the sweet or umami heteromeric taste receptor in vitro, they do not elicit a demonstrable or desired effect on sweet or umami taste in humans.
One way of potentially alleviating such “false positives” is the use of cells that endogenously express the T1R2/T1R3 or T1R1/T1R3 receptors rather than recombinant cells as these cells may be less susceptible to interacting with non-physiologically relevant compounds. The present invention provides another means for eliminating such “false positives” in screening assays using the T1R2/T1R3 sweet receptor which has been demonstrated with numerous compounds to be highly reliable.